
#include <string>
#include <vector>

using namespace std;

class Solution {
public:
    void reverseString(vector<char> &s) {
        int left = 0;
        int right = s.size() - 1;
        while (left <= right) {
            char tmp = s[left];
            s[left++] = s[right];
            s[right--] = tmp;
        }
    }
};